Purification of cellulose esters



Patented Mar. 31', 1931 UNITED STATES FRIEDRICH OLSEN, F DOVER, NEW JERSEY PURIFICATION OF CELLULOSE ESTEBS Ho Drawing.

Application filed March 1, 1929. Serial No. 343,832.

(GRANTED UNDER THE ACT OF MARCH 3, 1883, AS AMENDED APRIL 80, 1928; 370 0. G. 757

The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to the purification 7 pounds of cellulose less stable than the cellulose nitrate which it is desired to produce in a stable serviceable form.

Most of the purification process in vogue either follow directly or are modifications of the standard process in which the nitrocellulose receives at least 40 hours boiling with not less than four changes of water, no alkali being used in this boiling. The actual procedure consists of a preliminary boil of 16 hours duration in sour water, the acidity of which is about 0.1 to 0.3 per cent calculated as H SO followed by three-8 hour boils, each with changed water. After this preliminary boiling treatment of at least 40 hours total time, the nitrocellulose is pulped for the purpose of reducing the pyrocotton fibres to a uniform state of division in order to remove the last traces of acidity occluded by the fibres. The preliminary boilingtub treatment reduced the acidity of the fibres and of the interstitial material, but the pulping process, by macerating these fibres, has set free an ad itional amount of acid. It is, therefore, necessary to repurify the pyrocotton by boiling. The poaching treatment comprises a 6 hour boiling in water which usuallycontains a small amount of dissolved sodium carbonate followed by a 2 hour boiling and four one-hour boils and finally ten cold water washes; all boils and washes being with fresh water. The total period of boiling is therefore 52 hours.

To standard tests are used for the purpose of determining the degree of purification 5 which is achieved by these various boils and linters are used as a raw material.

purities present in the form ofcombined acids of the character of cellulose sulphate.

I have discovered that a marked reduction in the time of purification can be effected with a corresponding saving and cost, due to the reduced amount of Water required for purification, and consequent reduction in labor involved, by carrying out the pulping operation prior to tie hydrolyzing boils. When the pulping treatment is properly carried out there is offered to the action of the purifying wash water a surface many times greater than that exposed prior to pulping. There may even be achieved by the pulping operation an improved means of access to the internal walls of the tubular cotton hair, when cotton It is ap-. parent from the results of the normal methyl violet test at 135 (1, that a complete decomposition of the unstable esters or combined acids has not been accomplished by thecustomary hydrolytic boils prior to pulping, and that the increased surface exposed by the pulping has enabled a' further decomposition of the undesirable impurities to be made. Not only, therefore, is the removal of the impurities of the combined acid type facilitated by pulping prior to the hydrolytic boils, but it is also possible to effect this purification more completely, so that the resulting nitrocellulose is a material of higher stability than could be achieved from the same degree of purification had the pulping process not preceded the hydrolytic boils.

As one example of the'manner in which the improved process may be conducted, the following procedure is given:

The charge of nitrocellulose which has been drowned in water after discharging from the centrifuge is either removed from the bulk of the sour water by draining, decanting, centrifuging, or by similar suitable means, in order to efiect the removal of as much of the acid as can readily be accomplished with a very little effort; or the nitrocellulose ,is given such washing as will reduce the acidity to approximately 1% or less based on the weight ofnitrocellulose present. The nitrocellulose is then pulped in any suitable type of beating machine. Sodium carbonate, calcium carbonate or other suitable agent may be added, if desired, to neutralize the acid liberated during the pulping, but the use of such alkaline reagents is not necessary if the metal of the pulping machine is unaliected by the acid. The pulping is continued until the desired increase in exposed surface has been accomplished as judged by the commonly known fineness test, or preferably by microscopic examination, after which. the nitrocellulose is subjected to a series of boils and washes until the desired degree of purifica' tion has been achieved. This purification treatment usually comprises a boil in water, the acidity. of which is controlled to approximately 0.25%, but it has been found that less than half of the 16 hours sour boiling usually employed will sufiice for obtaining the desired degree of purity when followed by alternating boils in fresh water and washes with cold fresh Water, again less than half of the amount of boiling being sufficient. Complete stability as judged by fulfilling the requirements laid down for stability having been obtained with less than 20 hours total time of purification.

I claim:

1. The process of purifying cellulose esters which consists in first pulping the cellulose esters, then boilin it for approximately eight hours in water, the acidity of which is controlled to approximately 0.25%, and then subjecting it to alternate boils and washes in fresh water for approximately twelve hours.

2. The process of purifying cellulose esters which consists in first pulping the cellulose subjecting it to alternate boils and washes and washes in fresh water for approximately twenty hours.

3. The steps in the process of preparing nitrocellulose which consists in nitrating cellulose, pulping, and then alternately boiling and washing in water.

FREDRICH OLSEN. 

